1. Technical Field
The present disclosures relate to an image scanning apparatus.
2. Related Art
Generally, an image scanning apparatus employs a white reference member as a light distribution reference member to be used for a shading correction. When scanning is executed, an image of an original sheet passing over the white reference member is scanned. When the white reference member is used, however, there may occur a show-through phenomenon which is a phenomenon that a change in thickness of color on a back surface of the original sheet affects scanning of an image formed on a front surface of the original sheet. In order to reduce such a show-through phenomenon, image scanning apparatuses employing the gray reference member, which has a smaller reflection coefficient than the white reference member, have been suggested recently.
An example of such an image scanning apparatus employs a non-white reference member which is provided as a guide for the original sheet in a sheet conveying device. In such an image scanning apparatus, the shading correction is performed, based on the reflection coefficient of the non-white reference member, so that a reflection density obtained by scanning the non-white reference member has substantially the same quantity as a reflection density obtained by scanning the white reference member. When an image on the original sheet, which is conveyed by the conveying device, is scanned, the shading correction is applied based on the reflection density compensated as above.